Potassium along with phosphorous and nitrogen are major plant growth nutrients. As a commercial source of potassium, potash ores form the basis for the manufacture of fertilizers for the agriculture industry. The most important potash ore, sylvinite, contains sylvite (KCl) and halite (NaCl), and these two minerals are commonly separated by flotation carried out in saturated brine. Primary long-chain amines are exclusively utilized to float sylvite from halite.
Sylvinites may contain up to 15% of insoluble gangue minerals (anhydrite, dolomite, clays, etc.), which must be removed prior to floating sylvite either by mechanical means, or by selective flocculation-flotation. Desliming is followed by sylvite/halite differential flotation commonly preceded by classification of the ore into coarse and fine streams which are conditioned separately with the flotation reagents. In the case of flotation of fines, the reagents include long-chain amine collector and frother; in the case of coarse fractions flotation, an extender oil is utilized along with long-chain amines and a frother. In commercial practice, widely adopted ESSO 904 brand oil is used as an extender oil; frothers are added to the pulp last, just before flotation following conditioning with all reagents.
The solubility of long-chain aliphatic amines in water is very low and further decreases in brine. Since the Krafft points for long-chain amines in brine significantly exceed temperatures at which commercial potash flotation plants operate (10.degree.-35.degree. C.), such amines in brine appear in the form of colloidal species (J. S. Laskowski, Flotation of Potash Ores, SME Symposium Reagents for Better Metallurgy, Albuquerque, February, 1994). The evidence advanced by several researches (J. Leja, in Potash Technology, Pergamon Press, Toronto, 1983, pp. 623-629) suggests that such colloidal species are responsible for the flotation of sylvite particles. Colloidal dissolution of amines is clearly affected by surfactants such as alcohols (A. W. Ralston & C. W. Hoerr, J. Am. Chem. Soc., vol. 68, pp. 851-854, 1946; H. M. Alexandrovich et al., in Flotation Reagents, Nauka, Moscow, 1986, pp. 170-176). According to J. Leja, the rate of spreading of amine films at the air/liquid interface, very low in brine, sharply increases in the presence of alcohols.
Aliphatic amines are also used as metal corrosion inhibitors (U.S. Pat. No. 2,460,259). Since long-chain amines are nearly insoluble in water, the deposition of a protective film of a corrosion inhibiting substance, such as octadecylamine, confronted a number of problems. The use of dispersing/emulsifying aids to prepare corrosion inhibitor dispersions was found to be beneficial. Examples of several patented additives have been listed below: polyalkoxylated derivatives of monocarboxylic acids and alkyl phenols (U.S. Pat. No. 2,649,415), condensates of aliphatic amines with ethylene oxide (U.S. Pat. Nos. 2,956,889 and 3,418,253) and other amine derivatives (U.S. Pat. Nos. 3,029,125, 3,378,581 and 3,860,430).
In order to increase fatty amine dispersability in water, it has been suggested in U.S. Pat. No. 2,816,870 to dissolve the fatty amine in an alkoxyalkanol solvent and use either a cationic or non-ionic dispersing agent. Another patent (British Patent No. 1,038,860) suggests the use of quaternary ammonium salt emulsifiers to enhance the dispersability of fatty amines in water.